Help Wanted Translate OpenGL code to Unity's way

Hey, I've been trying to port an old MMORPG client to Unity, the unfamous Ragnarok Online. Among many things, the clients reads its effects from files, which are now known to the community and we've been able to parse them. Fast forward to my problem, I do not know anything about OpenGL and my main reference is written on top of OpenGL, so I've decided to come here and ask you guys if you would help me translate the OpenGL code to Unity's way of doing graphics. Any help would be appreciated, that includes explanation of what the following code does.

Here's the function responsible for rendering:

Spoiler: JavaScript function

Code (JavaScript):

1. /**
2.      * Setup geometries, send data to GPU
3.      *
4.      * @param {object} webgl context
5.      * @param {glTexture} webgl texture
6.      * @param {StrAnimation} animation object
7.      */
8.     StrEffect.prototype.renderAnimation = function renderAnimation( gl, material, anim )
9.     {
10.         var uniform   = _program.uniform;
11.         var attribute = _program.attribute;
12.  
13.         // Update geometries
14.         _bufferData[0]  = anim.xy[0];
15.         _bufferData[1]  = anim.xy[4];
16.         _bufferData[2]  = 0; //anim.uv[0];
17.         _bufferData[3]  = 0; //anim.uv[1];
18.  
19.         _bufferData[4]  = anim.xy[1];
20.         _bufferData[5]  = anim.xy[5];
21.         _bufferData[6]  = 1; //anim.uv[2];
22.         _bufferData[7]  = 0; //anim.uv[3];
23.  
24.         _bufferData[8]  = anim.xy[3];
25.         _bufferData[9]  = anim.xy[7];
26.         _bufferData[10] = 0; //anim.uv[4];
27.         _bufferData[11] = 1; //anim.uv[5];
28.  
29.         _bufferData[12] = anim.xy[2];
30.         _bufferData[13] = anim.xy[6];
31.         _bufferData[14] = 1; //anim.uv[6];
32.         _bufferData[15] = 1; //anim.uv[7];
33.  
34.         if (anim.angle !== _lastAngle) {
35.             mat4.identity(_matrix);
36.             mat4.rotateZ( _matrix, _matrix, - anim.angle / 180 * Math.PI );
37.             _lastAngle = anim.angle;
38.         }
39.  
40.         anim.pos[0] -= 320;
41.         anim.pos[1] -= 320;
42.  
43.         // Send effect parameters
44.         gl.uniform4fv( uniform.uSpriteColor,    anim.color );
45.         gl.uniform2fv( uniform.uSpriteOffset,   anim.pos );
46.         gl.uniform3fv( uniform.uSpritePosition, this.position );
47.  
48.         gl.uniformMatrix4fv( uniform.uSpriteAngle, false, _matrix );
49.  
50.         // Send new buffer
51.         gl.bindBuffer( gl.ARRAY_BUFFER, _buffer );
52.  
53.         // Link attribute
54.         gl.vertexAttribPointer( attribute.aPosition,     2, gl.FLOAT, false,  4*4, 0*4 );
55.         gl.vertexAttribPointer( attribute.aTextureCoord, 2, gl.FLOAT, false,  4*4, 2*4 );
56.  
57.         gl.bufferData( gl.ARRAY_BUFFER, _bufferData, gl.STREAM_DRAW );
58.  
59.         // Send texture and data
60.         gl.blendFunc( D3DBLEND[anim.srcalpha], D3DBLEND[anim.destalpha] );
61.         gl.bindTexture( gl.TEXTURE_2D, material );
62.         gl.drawArrays( gl.TRIANGLE_STRIP, 0, 4 );
63.     };

Full code can be found at Github and the project I'm working is also open-source and can be found here.

Thank you!